This invention relates generally to a surgically implantable physiological shunt systems and related flow control devices. More particularly, the present invention relates to shunt systems including one-way flow control devices for controlling the flow of cerebrospinal fluid out of a brain ventricle and preventing backflow of fluid into the brain ventricle, and processes for manufacturing such devices.
In the medical arts, to relieve undesirable accumulation of fluids it is frequently necessary to provide a means for draining a fluid from one part of the human body to another in a controlled manner. This is required, for example, in the treatment of hydrocephalus, an ailment usually afflicting infants or children in which fluids accumulate within the skull and exert extreme pressure and skull deforming forces.
In treating hydrocephalus, cerebrospinal fluid accumulated in the brain ventricles is typically drained away utilizing a drainage or shunt system including a catheter inserted into the ventricle through the skull, which is connected to a tube which conducts the fluid away from the brain to be reintroduced into the peritoneal cavity or into the vascular system, as by extending a distal catheter through the patient's jugular vein to the atrium portion of the heart. To control the flow of cerebrospinal fluid and maintain the proper pressure in the brain ventricle, a pump or valve is placed in the conduit between the brain and the peritoneal cavity or the heart. An exemplary flow control device is found in U.S. Pat. No. 4,560,375.
Although such drainage systems have provided successful results, a problem of over drainage of the cerebrospinal fluid from the brain ventricles sometimes exists. Over drainage of cerebrospinal fluid may result in excessive reduction of the cerebrospinal fluid pressure within the brain ventricles and predispose the development of a subdural hematoma or hydroma, and excessive reduction of ventricular size leading to shunt obstruction because of impingement of the ventricular walls on the inlet holes of the ventricular catheter. This over drainage can be caused by the siphoning effect of hydrostatic pressure in the distal shunt catheter. The siphoning effect of hydrostatic pressure may be created by the elevation of the ventricular catheter inlet with respect to the distal catheter outlet (i.e., when the patient sits, stands or is held erect). In order to prevent such over drainage caused by the siphoning effect of hydrostatic pressure in the distal shunt catheter, siphon control devices have been placed in the conduit, typically between the flow control device and the peritoneal cavity or the heart. An exemplary siphon control device is found in U.S. Pat. No. 4,795,437.
In the past, a physician desiring to include both a flow control device having a pump or valve, and a siphon control device has been required to link the two separate components by surgical tubing or the like during the surgical procedure. The addition of separate flow control elements into a shunt system has several drawbacks, including the lengthening of surgery time required to implant the shunt system, compatibility problems of devices produced by different manufacturers, and the introduction of potential shunt separation and/or leak sites where the separate components are connected to one another via the surgical tubing.
In order to solve these and other related problems, it has been proposed to combine two or more functional elements into a single fluid flow control device. It has been found, however, that such combination-type flow control devices cannot be manufactured as an integral unit utilizing standard medical implant manufacturing techniques.
Accordingly, there has been a need in the medical arts for an implantable fluid flow control device which can be assembled in accordance with a simplified process to provide the flow control characteristics previously obtainable only by connecting, in series, two or more shunt system devices. Such physiological drainage devices for controlling the flow of fluid from one part of the body to another must be relatively inexpensive to manufacture and capable of being constructed substantially of non-metallic parts which are not subject to adhering to one another and causing a malfunction of the device. A combination flow control device is needed which includes a one-way flow control valve for controlling the flow of cerebrospinal fluid out of the brain ventricle and preventing backflow of fluid into the brain ventricle, and permits fluid flow therethrough only when upstream fluid pressure exceeds downstream fluid pressure by a selected pressure differential.
Additionally, a novel assembly process for flow control devices utilized in physiological shunt systems is needed wherein separate functional components of the device can be manufactured separately and assembled together in a simplified procedure to produce a reliable and economical product. Such a device may utilize two separate functional bases which can be connected to one another in a manner ensuring no relative tensile or torsional movement, and invested within a housing to define the desired fluid flow path through the device. Such an assembly process should minimize the possibility of any unintended fluid leakage from the device, and preferably require no adhesive to secure the bases to one another. As will become apparent from the following description, the present invention satisfies these needs and provides other related advantages.